1. Field of the Invention
The present invention relates to a gas-discharge tube in which a discharge gas is sealed as a discharge medium and to a display apparatus that can display images, (video image), including a dynamic image, by aligning a large number of such gas-discharge tubes in parallel form.
2. Description of Related Art
Large scale display apparatuses have been proposed wherein a gas-discharge tube is constructed such that a phosphor is provided inside of a long and narrow transparent insulating tube and a discharge gas is sealed in the tube in the same manner as PDP (Plasma Display Panel) using the same illumination principle and wherein a large number of such gas-discharge tubes are aligned in parallel form and thereby video images, including a dynamic image, can be displayed (see, for example, Japanese Patent Application Laid-Open No. 61-103187 (1986)). Such a display apparatus is a self-emission type display apparatus that can display a video image of high luminance and can realize a large display exceeding a one hundred inch display, and therefore, is preferable in the case when an entire indoor wall is used as a display apparatus.
FIG. 1 is a schematic perspective view showing one example of a conventional display apparatus utilizing gas-discharge tubes and FIG. 2 is a schematic cross-sectional view showing the structure of the display apparatus along line X-X of FIG. 1. In the following, the conventional display apparatus and the gas-discharge tubes utilized therein are described in reference to FIG. 1 and FIG. 2. Here, gas-discharge tubes having a rectangular cross-section are disclosed in the above described Japanese Patent Application Laid-Open No. 61-103187 (1986) while gas-discharge tubes having a circular cross-section are utilized in the conventional example shown in FIG. 1 and FIG. 2.
The conventional display apparatus 80 has a large number of gas-discharge tubes 90, 90, . . . aligned in parallel form in the direction perpendicular to the direction of their axes and has a structure wherein these gas-discharge tubes 90, 90, . . . are sandwiched between a rear support member (substrate) 96 and a front support member (substrate) 98. Address electrodes (also referred to as selection electrodes) 97, 97, . . . are provided in the direction of the axes of gas-discharge tubes 90, respectively, on the surface of the gas-discharge tube 90 side of the rear support member 96. On the other hand, sustain electrodes (also referred to as display electrodes) 99, 99, . . . whose longitudinal direction is in a direction that crosses the direction of the address electrodes 97 in the plan view are provided with predetermined intervals on the surface of the gas-discharge tube 90 side of the front support member 98. Here, each of the sustain electrodes is formed of a pair of electrodes 99a and 99b. 
In each gas-discharge tube 90, a glass tube 91, having light transmission properties in a hallow cylindrical form, which is a long and narrow transparent insulating tube having an internal diameter of, for example, 0.8 mm and a thickness of 0.1 mm is utilized. A secondary electron emission film (also referred to as a protection film) 92 for lowering the level voltage (discharge voltage) required for the occurrence of discharge is formed to have a uniform film thickness on the inner side of glass tube 91. Furthermore, a phosphor support member 94 in approximately C shape in the cross section across the axis is provided on the inner side of the secondary electron emission film 92. Moreover, a phosphor layer 93 that excites a vacuum ultraviolet light (ultraviolet light) generated by discharge to a visible light is formed on the portion of rear support member 96 side of the inner surface of phosphor support member 94. In addition, a discharge gas 95 such as Xe—Ne or Xe—He is sealed inside of glass tube 91.
Each region defined by an address electrode 97 and each pair of sustain electrodes 99a and 99b, which cross each other, forms a unit emitting region (cell). One of the pair of sustain electrodes 99a and 99b is used as a scan electrode such that a voltage is applied between this scan electrode and address electrode 97 and thereby an address discharge (opposed discharge) for a on-state writing selectively occurs so that a wall charge occurs on the inner wall of glass tube 91 that corresponds to the cell where this address discharge has occurred. Subsequently, a voltage is applied between the pair of sustain electrodes 99a and 99b and thereby a on-state discharge (surface discharge) for a on-state sustain occurs in the cell where the wall charge has occurred due to the address discharge. This on-state discharge makes Xe in the discharge gas to collide with an electron so that an ultraviolet light is emitted. The ultraviolet light is excited to a visible light by means of phosphor layer 93 and this visible light is emitted to the outside. In this manner, an electrical field in each cell is controlled in accordance with voltages applied to sustain electrodes 99a, 99b and address electrode 97 and thereby the occurrence of an ultraviolet light is controlled so that the conventional display apparatus can display a video image of high luminance.
In the conventional display 80 shown in FIG. 1 and FIG. 2, however, the rear support member 96 and the front support member 98 are arranged in a condition where they sandwich glass discharge tubes 90, 90, aligned in parallel form. As a result, in some cases a gap A generates between adjacent gas-discharge tubes 90 and 90. In such a case, a dispersion occurs at distance X between an address electrode 97 provided on the rear support member 96 with a predetermined dimension precision by use of a technique, such as photolithography, and center line B of each gas-discharge tube 90 and, therefore, a problem arises wherein the amount of the opposed discharge and the region of the occurrence of the opposed discharge differ from each cell. In addition, even in the case where discharge tubes 90 are aligned in such a manner as to prevent gap A from occurring, a dispersion of the external diameter can easily occur in glass tubes 91 having circular cross sections in comparison with address electrodes 97, 97, . . . that can be easily maintained at equal intervals and, therefore, there is a fear that the same situation as described above may occur.
In particular, when the gas-discharge tube 90 has a circular external shape as shown in FIG. 1 and FIG. 2, there is even a fear where an address electrode 97 and the external surface of a glass tube 91 do not make a direct contact with each other in the case where the above described distance X becomes large. In such a case, air having an extremely low dielectric constant intervenes between the external surface of the glass tube 91 and the address electrode 97 and, therefore, a voltage that must be applied to address electrode 97 in order to make an opposed discharge occur becomes high. In the case where the voltage that must be applied to address electrode 97 in order to make this opposed discharge occur becomes higher than the voltage that can be applied to address electrode 97, it becomes impossible to make the opposed discharge occur resulting in a problem where a display defect occurs.
In addition, the secondary electron emission film (metal oxide film such as magnesium oxide or alumina) 92 prevents ion impact to glass tube 91 functioning as a dielectric and at the same time plays an important role such as emitting secondary electrons for the discharge. As for a method for forming such secondary electron emission film 92, a method (coating thermal decomposition method) has been widely and conventionally used where a solution (liquid to be coated) containing organic fatty acid salt (for example, fatty acid magnesium) is introduced inside of the glass tube 91 so as to be coated to the inner surface thereof, and the liquid that has been coated is baked so that the secondary electron emission film 92 is formed on the inner surface of glass tube 91.
It is preferable for gas-discharge tube 90 utilized in the display apparatus 80 to have a short opposing distance between address electrode 97 and sustain electrode 99a (99b) in glass tube 91 in order to lower the voltage required for the occurrence of the opposed discharge for the purpose of cost reduction, lowering of the consumed power and the like. In the case where the cross section across the axis of glass tube 91 has a circular inner peripheral shape (hereinafter referred to as a cylindrical tube) as shown in FIG. 1 and FIG. 2, the surface tension applied to the coated liquid becomes uniform and therefore, secondary electron emission film 92 having approximately uniform film thickness distribution can be formed. However, in the case where the above described gas-discharge tubes having a rectangular cross section as disclosed in Japanese Patent Application Laid-Open No. 61-103187 (1986) are utilized, the surface tension applied to the coated liquid becomes non-uniformed due to the inner peripheral shape of the cross section across the axis of the glass tubes being rectangular (including the case of being approximately elliptical) and therefore the coated liquid tends to collect to regions (bent portions) having a smaller curvature radius due to capillarity. Accordingly, in the case where glass tubes which are not cylindrical tubes as disclosed in Japanese Patent Application Laid-Open No. 61-103187 (1986) are used, the film thickness of the secondary electron emission film 92 in the bent portions of the cross section of the glass tubes becomes large while the film thickness of the secondary electron emission film 92 in the regions having a great curvature radius becomes small.
As described above, it is preferable for gas-discharge tubes utilized in the display apparatus 80 to have a glass tube 91 where the opposing distance between the address electrode 97 and the sustain electrode 99a (99b) is short. As a result, in the case where glass tubes which are not cylindrical tubes are utilized, the address electrode and the sustain electrode are formed such that the curvature radius in the glass surface (side surface) that defines the opposing distance between the two is smaller than the curvature radius in the glass surface (discharge surface) on the sustain electrode 99a (99b) side, which is a surface discharge region. As a result of this, a problem arises wherein the secondary electron emission collects to the side surface in the configuration while the secondary electron emission efficiency deteriorates leading to a rise of the sustain voltage in the glass surface on the sustain electrode side due to the reduction in the film thickness of the secondary electron emission film 92.
On the other hand, the phosphor support member 94 is generally manufactured by a redraw method wherein a glass tube is processed in advance to have a shape such that the cross section thereof has a shape approximately similar to the desired shape and then the processed glass tube is heat stretched. However, in the case of the phosphor support member 94 where the cross section thereof is not point symmetrical, the tension at the time of the heat stretching does not become uniformed causing deformation easily. Accordingly, distance Y between the inner surface (discharge surface) on the sustain electrode 99a (99b) side, which is a region where a surface discharge occurs, and the phosphor support member 94, that is to say, the phosphor layer 93 becomes large, which causes a problem wherein the excitation efficiency is reduced when the ultraviolet light having been generated by the charge excites the phosphor layer 93 and the brightness is reduced.